As with most technologies, the best of plans starts to fall apart when faced with the incompetence or malice of users. Web authors started setting every link to open within the content panel of their own website, even if they were linking to another person's page. The result was locking other peoples' websites in a cage of banners and navigation frames for another person's homepage.
This became such a problem that a link appeared at the bottom of many website's homepages for the sole purpose of reopening the page in the main browser window. This would effectively get rid of any frames left over from another web author's site.
Of course, websites made for modern users have to take into account that the majority of web traffic now occurs over mobile devices. Frames are buggy at best and obscure content completely at worst when viewed on smartphone displays. As such, with the HTML5 specification, frames were deemed obsolete, although iframes (internal frames) are still allowed for now.